Source : WordNet®

undercover
     adj : conducted with or marked by hidden aims or methods;
           "clandestine intelligence operations";
           "cloak-and-dagger activities behind enemy lines";
           "hole-and-corner intrigue"; "secret missions"; "a
           secret agent"; "secret sales of arms"; "surreptitious
           mobilization of troops"; "an undercover investigation";
           "underground resistance" [syn: {clandestine}, {cloak-and-dagger},
            {hole-and-corner(a)}, {hugger-mugger}, {hush-hush}, {on
           the quiet(p)}, {secret}, {surreptitious}, {underground}]